TUESDAY, Oct. 21, 2014 (HealthDay News) -- Children of mothers exposed to high levels of traffic air pollution during pregnancy may be at increased risk for lung damage, according to a new study.

Researchers tested the lung function of 620 children in Spain when they were 4 years old. Their mothers' exposure to the traffic air pollutants nitrogen dioxide and benzene during the second trimester of pregnancy was also assessed.

Compared to children born to mothers exposed to less traffic air pollution, the risk of impaired lung function was 22 percent higher in youngsters of mothers exposed to high levels of benzene and 30 percent higher in children whose mothers were exposed to high levels of nitrogen dioxide.

The link between exposure to high levels of traffic air pollution during pregnancy and lung damage was strongest among poorer children and those with allergies.

There was no significant evidence of a connection between exposure to air pollution in the first year of life and a child's risk of impaired lung function at preschool age, according to the study published Oct. 20 in the journal Thorax.

The findings suggest, but don't prove, that exposure to traffic-related air pollutants during the prenatal period could adversely impact the developing lung, Dr. Eva Morales, of the Center for Research in Environmental Epidemiology in Spain, and colleagues wrote.

"Public policies to reduce exposure to traffic-related air pollution may avoid harmful effects on lung development and function with substantial public health benefits," the researchers said in a journal news release.

The study offers convincing evidence that exposure to pollution before birth has long-term effects on children's lungs, Dr. Peter Sly, professor at the Queensland Children's Medical Research Institute at the University of Queensland, Australia, wrote in an accompanying editorial.

These and similar findings show policy makers that "limiting exposure to traffic-related pollution during fetal development and early postnatal life is one way that the burden of respiratory disease can be decreased," he said.